Method for improving coating receptivity of an aluminum surface and resultant article



United States Patent METHOD FOR IMPROVING COATING RECEPTIV- ITY OF AN ALUMINUM SURFACE AND RE- SULTANT ARTICLE Ehrlich M. Eiland, Lower Burrell, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa., 21 corporation of Pennsylvania No Drawing. Filed July 14, 1959, Ser. No. 826,929

11 Claims. c1. 117 49 This invention relates to treatment of aluminum surfaces, and more particularly to treatments for improving the receptivity of aluminum surfaces to various coatings. Aluminum, as generally used herein, embraces both aluminum of various commercial grades and aluminum (base alloys.

The commercial applications of aluminum sheet and foil have been continually increasing, and there is a growing market for aluminum, for example, in labeling and packaging. Consequently, it has become necessary to economically render aluminum surfaces, particularly in as-rolled tempers, receptive to adhesion of conventional oleaginous and organic-solvent type printing inks, adhesives, lacquers, plastic films and other adhesively applied coatings.

Copious amounts of oil are commonly employed in the rolling of aluminum sheet and foil, and the aluminum surfaces retain substantial amounts of residual rolling lubricant on and in the natural films of oxide present on such surfaces. Consequently, many commonly used printing inks, wash coats and adhesives, for example, exhibit little or no adhesion to an oily aluminum surface and may be easily stripped or lifted from the surface. In fact, by far the most objectionable characteristics of as-rolled surfaces preventing adhesion of coatings, are attributed to the residual rolling lubricant. Consequently, it is generally necessary to remove residual rolling lubricant from the aluminum surface or to counteract the lubricant chemically. It is important, for most applications, that such treatment does not adversely afiect the surface appearance of the metal.

It is a general object of this invention to provide a method for improving the coating receptivity of aluminum surfaces having residual rolling lubricant thereon.

It is a more specific object of this invention to provide a method of treating aluminum surfaces having residual rolling lubricant thereon and thereby improve the receptivity of such surfaces to various adhesively applied coatings, including plastic films, adhesives, inks, lacquers or other protective or decorative matter.

Other objects and advantages of the invention will become evident in the following description thereof.

According to the present invention, an aluminum surface having residual rolling lubricant thereon is treated with phytic acid. It has been found that treatment of aluminum surfaces with phytic acid imp-arts to the surface the property of being wetted by various coatings, and is particularly useful for the treatment of lubricant bearing, as-rolled aluminum foil and sheet. Such treatment improves the receptivity of the aluminum surface to adhesion of various coatings, which coatings include non-aqueous oleaginous and organic-solvent type printing inks, adhesives, dewaxed shellac, nitrocellulose and vinyl lacquers, plastic films, and other similar protective or decorative matter.

' Phytic acid is generally available in concentrated form (70% by weight) and may be diluted with a suitable solvent, preferably a volatile solvent. Organic solvents, particularly light weight organic solvents such as ethyl 2,976,170 Patented Mar. 21, 1961 alcohol or a mixture of isopropyl alcohol and. Cellosolve, are especially desirable. A phytic acid primer may be applied to the aluminum surface at room temperature by any suitable means such as rolling, brushing, spraying and the like. The preferred minimum concentration of phytic acid in solution is somewhat dependent upon the surface condition of the metal, the surfaces having large amounts of residual rolling lubricant requiring a greater concentration of phytic acid in the solution. However, the concentration of phytic acid in the solution applied to the aluminum surface is preferably at least 0.02% by weight. Generally it is not necessary to exceed about 10% by weight. In any event, the optimum concentration for yielding a surface highly receptive to printable matter and other coatings may be readily determined through simple experimentation.

The treated aluminum surface may be dried at elevated temperatures to facilitate economic and rapid processing. Solvents for phytic acid that are readily volatile, such as ethyl alcohol or a mixture of.isopropyl alcohol and Cellosolve are, therefore, preferred. The conditions for drying will, of course, vary, and may be left to the choice and needs of the individual. 1 However, it is neither necessary nor ordinarily desirable to dry at a temperature that may result in annealing of the metal. Generally, an aluminum surface treated with phytic acid in ethyl alcohol solution may be dried at about 150 to 450 F. in about 5 seconds to 2 minutes.

The initially oily aluminum surface, treated in accordance with my invention, is highly receptive to such conventional non-aqueous oleaginous and organic-solvent type printing inks as rotogravure, fiexographic and lithographic inks, as well as to emulsion type adhesives, plastic films, and to nitrocellulose, dewaxed shellac and vinyl wash coatings. In fact, the treated aluminum retains good receptivity to a variety of such coatings even after several weeks of storage. In the case of aluminum foil supplied in coil'form, it may be desirable to treat both surfaces of the metal with a phytic acid solution to avoid contamination of the treated surface by contact with the untreated surface on rewinding. On the other hand, it may be quite satisfactory to apply phytic acid only to one side of the metal when the metal is fed directly to a printing or coating apparatus, or when the treatment proceeds to or from a laminating step.

Many conventional resinous wash coats, such as nitrocellulose lacquer and dewaxed shellac, will not adhere to an aluminum surface bearing a rolling lubricant. However, a number of printing inks commonly employed in the decorating metal surfaces are particularly adaptable for application to an aluminum surface when a resinous wash coat has been applied thereto, and the wash coat minimizes the loss of adhesion due to offsetting from paper as in the case of a foil-paper laminate wound in coil form. In accordance with my invention, an oily aluminum surface may be treated with phytic acid and the wash coat subsequently applied, or phytic acid may be incorporated in the wash coat and the resultant blend applied to the metal surface. In either case, by reason of the phytic acid treatment, the wash coat is retained on the aluminum surfacewhich may be further coated with conventional printing inks, adhesives and the like. Similarly, the phytic acid may be added to other adhesively applied coatings, and the treatment efiected at the time of application to the metal as in printing with a phytic acid containing ink.

Example I As-rolled aluminum foil of 99.45% purity, and 0.0007

inch thick, was treated with a 0.25% solution of concentrated phytic acid in ethyl alcohol, and the treated surface dried at 200 F. for 15 seconds. The treated foil surface exhibited excellent receptivity to fiexographic printing ink, and to nitrocellulose lacquer wash coat.

Example I] The procedure of Example I was repeated except that a 0.25% solution of concentrated phytic acid was added to a polyvinyl butyral lacquer, and the coating applied to the as-rolled foil surface. The vinyl coating was strongly retained by the foil surface.

Example III The treatment of Example I on as-rolled foil was repeated using a 5% solution of concentrated phytic acid. Nitrocellulose lacquer was then applied to the treated surface and dried at 200 F. for seconds. The treated surface was found to have excellent receptivity and re tention of lithographic ink.

Example IV The procedure of Example III was repeated except that the as-rolled foil was first treated with a solution of 0.25% concentrated phytic acid and 0.25% dewaxed shellac in ethyl alcohol and then the nitrocellulose lacquer applied. The treated surface was found to be receptive to lithographic printing.

Example V Aluminum sheet 0.065 inch thick having a nominal composition of 4% copper and 0.5% manganese and magnesium, in a hard temper, having residual rolling lubricant on the surfaces, was treated with a solution of 0.25% concentrated phytic acid and 0.25% dewaxed shellac in ethyl alcohol. The sheet was dried at 200 F. for one minute. Conventional rotogravure and fiexographic inks, and nitrocellulose lacquer adhered satisfactorily to the treated surface.

Example VI Example VII As-rolled aluminum foil 0.0035 inch thick and 99.45% purity was treated with a solution of 0.25% concentrated phytic acid and 0.2.5 dewaxed shellac. When sufiiciently dried at room temperature, the treated surface was coated with Videne polyester plastic film manufactured and sold by Goodyear Tire and Rubber Company. Adhesion of the plastic film to the foil surface was found to be excellent.

Example VIII A conventional flexographic printing ink having added thereto 1.0% by weight concentrated phytic acid was applied to as-rolled aluminum foil 0.0035 inch thick and 99.45% purity, and the coating air dried at room temperature. The ink strongly adhered to the foil surface.

Example IX 0.00035 inch thick annealed aluminum foil of 99.45% purity, and having residual rolling lubricant thereon, was printed with a conventional rotogravure ink to which was added 1.2% by weight concentrated phytic acid.

Upon drying at room temperature, it was found that the ink adhered satisfactorily to the foil surface. The same ink containing no phytic acid would not adhere to the foil surface.

The treatment of aluminum surfaces bearing rolling lubricant with phytic acid should have extensive use in the packaging trade where it is necessary to print or otherwise decorate an aluminum foil overwrap. Such treatment will not dull or stain the metal surface so that a package, carton, or wrapper made from as-rolled foil which has been treated accordingly for ink receptivity will have an attractive bright surface.

As-rolled foil which has been surface treated in accordance with my invention may be used for other purposes than labeling and packaging, since many other uses for coating receptive aluminum surfaces will, of course, be obvious to those skilled in the art.

Having thus described my invention, I claim:

1. A method for improving the receptivity for adhesively applied coatings of an aluminum surface having residual rolling oil thereon which comprises treating said aluminum surface with phytic acid whereby the adhesion preventing characteristics of said oil are counteracted.

2. An aluminum surface treated in accordance with the method of claim 1, and characterized by being receptive to adhesion of applied coatings.

3. A method for improving the receptivity for adhesively applied coatings of an aluminum surface having residual rolling oil thereon which comprises treating said aluminum surface with a solution containing at least about 0.02% phytic acid whereby the adhesion preventing characteristics of said oil are counteracted.

4. A method for improving the receptivity for adhesively applied coatings of an aluminum surface having residual rolling oil thereon which comprises treating said aluminum surface with phytic acid in a volatile solvent whereby the adhesion preventing characteristics of said oil are counteracted.

5. The method according to claim 5 wherein said solvent is ethyl alcohol.

6. The method according to claim 4 wherein said solvent is a mixture of Cellosolve and isopropyl alcohol.

7. A method for improving the receptivity for adhesively applied coatings of an aluminum surface having residual rolling oil thereon which comprises applying to the aluminum surface the coating containing phytic acid whereby the adhesion preventing characteristics of said oil are counteracted.

8. A method for improving the ink receptivity to an aluminum surface having residual rolling oil thereon which comprises applying to the aluminum surface the ink containing phytic acid whereby the adhesion preventing characteristics of said oil are counteracted.

9. A method for improving the receptivity for adhesively applied coatings of an aluminum surface having residual rolling oil thereon which comprises treating said aluminum surface with a solution of phytic acid and a resinous wash coat whereby the adhesion preventing characteristics of said oil are counteracted.

10. Method according to claim 9 wherein said wash coat is dewaxed shellac.

11. Method according to claim 9 wherein said wash coat is nitrocellulose lacquer.

References Cited in the file of this patent UNITED STATES PATENTS 2,465,750 Reid Mar. 29, 1949 FOREIGN PATENTS 112,164 Australia Jan. 9, 1941 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent Noe 2,976,170 March 21, 1961 Ehrlich M. Eiland It is hereby certified'that error appears in the above numbered paten't requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 40, for the claim reference numeral "5"- read 4 Signed and sealed this 1st day of August 1961 (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents 

1. A METHOD FOR IMPROVING THE RECEITIVITY FOR ADHESIVELY APPLIED COATINGS OF AN ALUMINUM SURFACE HAVING RESIDUAL ROLLING OIL THEREON WHICH COMPRISES TREATING SAID ALUMINUM SURFACE WITH PHYTIC ACID WHEREBY THE ADHESION PREVENTING CHARACTERISTICS OF SAID OIL ARE COUNTERACTED. 